The present invention relates to a fiber optic laser conducting probe used for therapy for an early cancer known as a photodynamic therapy.
Photodynamic therapy for an early cancer is performed, while observing the body cavity with an endoscope, by irradiating a laser beam in the amount as necessary against the affected part with a fiber optic laser and diffusion probe inserted through a forceps aperture of the endoscope. It is necessary to provide, at the extreme end of the probe, a tip capable of carrying out the irradiation of a laser beam in response to shapes of the body cavity, such as tubular organs such as the throat and cervical canal, and bag-like organs such as the stomach and lungs. For that purpose, methods heretofore proposed include U.S. Pat. No. 4,693,556 and U.S. Pat. No. 4,660,925, in which a tip is formed at the extreme end by an ultraviolet hardening resin containing a fine powder of quartz to provide a uniform diffusion of light; U.S. Pat. No. 4,676,231, in which a transparent liquid with suspended fine particles is put into a hollow transparent tip; and U.S. Pat. No. 4,649,151, which suggests in its specification and drawings that an epoxy resin mixed with light diffusion particles are coated on an internal surface of a hollow transparent tip.
Especially in case a pulse wave laser beam is used, an end tip formed of an inorganic material (Examples: quartz, sapphire, glass, etc.) tends to be easily cracked and broken, which is dangerous when the concentration and high densification of shock waves generated from a pulse laser occur in the tip. A situation tends to occur in a tip which uses hard plastics (Examples: polymethylmethacrylate resin, polystyrene resin, etc.) that causes the inner surface of the tip to be blackened to deteriorate the light irradiating performance.
On the other hand, a tip made of polyacetal resin known as Derlin (a trademark of Du Pont) has the possibility of generating formalin, which is injurious to the living body due to the thermal decomposition by the laser.
We have previously proposed, in Japanese Utility Model Application No. 75579/1993, an end tip made of polyolefin resin, particularly, polyethylene resin. No inconvenience occurred in the end tip according to this proposal when it was used under the conditions such that an excimer dye laser having a wavelength of 630 nm was caused to be incident as a pulse laser having an intensity of 4 mJ to 8 mJ/pulse at a frequency of 40 to 80 Hz from the fiber end so as to have an outgoing energy of 600 J in total from the end tip. However, in the end tip according to the above proposal, when it is used by causing the above-described laser to be incident from the fiber end with a laser intensity of 8 mJ/pulse or more at a frequency of 80 Hz or more, it was found that the tip becomes thermally softened, expanded or bent due to the rise in temperature caused by the heating of the laser, and a blackening phenomenon due to the generation of free carbon sometimes occurs.
It is natural that for relieving the pains of a patient during therapy or for increasing the efficiency of the medical treatment, an intense laser beam is rapidly applied to irradiate the same amount of irradiation in the shortest period of time. The end tip should be improved accordingly. On the other hand, the damage of end tip due to the rapid application of the laser beam, particularly damage that is injurious to the patient, should be completely avoided. The end tip for collecting or diffusing a pulse laser beam should be selected very carefully, unlike the end tip for a continuous wave laser.